Electron discharge tube



Aug. 17, 1937. M. KNOLL ET AL ELECTRON DISCHARGE TUBE Filed March 6,1954 36 INVENTOR MAX ff/VOLL BY? OLF HULK/4 W TORNEY Patented Aug. 17,1937 PATENT OFFICE ELECTRON DISCHARGE TUBE Max Knoll and RudolfRzehulka, Berlin, Germany, assignors to Telefunken Gesellschaft fiirDrahtlose Telegraphic m. b. 11., Berlin, Germany, a corporation ofGermany Application March 6, 1934, Serial No. 714,261 In GermanyNovember 5, 1932 1 Claim.

The present invention relates to anelectron discharge tube for therectification, amplification and production of oscillations, and isprovided with a fiat cathode surface as the electron source. A fiatcathode is understood to be an incandes- -cent cathode of rectangular,square-shaped, or similarly formed section such as an ellipticalsection, the electron emitting surface of which forms a plane or nearlyplane surface. Discharge tubes provided with such cathodes, due to therelatively simple mounting of the cathode and of the electrode systemcooperating therewith, offer essential constructive advantages, andfurthermore afford obtaining of great steepness due to the relativelylarge cathode surface.

In such tubes it is advantageous to arrange the auxiliary electrodes,such as control grid and anode, in planesparallel to the cathodesurface.

Tests have proven that the actual steepness ofsuch arrangements is lessthan that when calculated from the emitting surface, and that thecharacteristic at its upward course does not reveal the required sharpbend (Flg. 1) but a smooth course (Fig. 2) so that the expected heightof the mutual conductance is not attained. The cause of this behavior isto be seen in the fact that with a definite control voltage of theelectrode system there corresponds respective locally different fieldintensities at the flat and curved or end portions of the cathodesurface.

- of the electrodes (for instance bars of a control This inventionresides in the fact that the electron emission from the narrow sides oredges of the cathode is suppressed, so that the emission is limited tothe plane or nearly plane parts of the cathode surface. In this mannerthe maximum steepness corresponding with the size of the emittingsurface, and a very sharp bend in the characteristic curve are obtained.The main object of the invention can best be accomplished by shieldingthe emission from the cathode edges or borders, by suitably shaping thecathode itself,

grid( opposite the cathode edges that the field intensity at the cathodeedges is greatly reduced or becomes negative in comparison with thefield intensity at the remaining cathode surfaces.

The accompanying figures show embodiments of the invention by way ofexample.

Figures 3 and 4 show front and plan views, respectively, of anembodiment of a triode in which the support rods 4 and 5 of the controlgrid serve as screens and simultaneously to reduce the field intensityat the cathode edges. The fiat cathode l which is of the indirectlyheated type, is fixedly secured in openings of insulating bridges l3 andI 4 by means of extensions 8, 9 and I0, I l at the upper and lower endsof the cathode, respectively. The grid support rods or bars 4 and 5 andthe anode supports I5 and I8 are also threaded through suitable openingsin the insulating bridges. The grid bars 4 and 5 are wide enough tocover the narrow sides 2, 3 of the cathode; the diameter of the rods andtheir distance from the narrow sides of the cathode is suitablyapproximately equal to the inner diameter of the grid.

Figure 5 shows a section through a pentode whose fiat cathode I1 is notcovered at the edges 21 and 31 by emitting substance. Only the widesurfaces of the cathode are provided with layers l2 of emittingsubstance. successively surrounding the cathode are control grid 51,screen grid 62, suppressor grid 63 and anode 11.

Figure 6 shows the section of a triode having a fiat cathode 2| whoseelectrical field in the direction of its two narrow sides or edges 22and 23 is extended by means of two auxiliary electrodes 24 and 25. Thecathode 2| and the auxiliary electrodes 24 and 25 are maintained at asuitable equal potential and are surrounded by control grid 26 and anode21.

Figure 7 represents a plan view of a triode having a square-shapedcathode 3i. Adjacent to the four corners 32', 33, 34 and 35 of cathode3| are the shields 31, 38, 39 and 40 which are connected to and serve tosupport the control electrode 36 placed between the anode 4| andthecathode.

What we claim is:

An electron discharge tube comprising an elongated indirectly heated,fiat-shaped cathode, substantially rectangular in cross section, aplurality of cooperating electrodes completely surrounding the cathodeand having their support rods in alignmentwith the narrower side edgesof the cathode, the support rods of the electrode immediately adjacentthe cathode being spaced from said cathode edges a distance equal tosubstantially the diameter of said rods, which diameter is substantiallywider than the cathode side edges, whereby to effectively shield thecooperating electrodes from electrons emitted from the

